14.1 Introduction

High voltage open bus, are air-insulated, current-carrying conductors, clamped to insulated supports as in the case of switchyards. Open busbars find applications both outdoors and indoors and in AC & DC systems. The present discussion will primarily focus on rigid Aluminium conductors installed in outdoor switchyards.

Before the introduction of the GIS (Gas Insulated Switchgear), a few high voltage switchyards in coastal areas (exposed to winds and salty atmosphere), and areas with heavy pollution had been housed in buildings. The high voltage lines entered and exited the building through high voltage condenser bushings or by cables.

Switchyards with a rigid bus are more compact with a low support structure and lesser phase to phase clearance when compared to those with strain bus. However, a strain bus offers better seismic force withstand capability than a rigid bus.

The cost of the Busbar (Aluminium alloy tubular conductor) as a percentage of the total cost of the switchyard equipment comprising circuit breakers, isolators, instrument transformers, surge arresters, line traps, insulators, and support structure is very small. Hence sizing of the busbar is always on the conservative size. Hot spots and corona discharges, if observed, can be attributed to improper selection and installation of clamps & connectors.

14.2 Description

These Busbars are primarily installed in the outdoor high voltage switchyards rated 36 kV and above. The rated voltage of AC & DC switchyards and transmission lines has reached the 1.5 million volts milestone.

Conductors in switchyards can be multi-layered and can be designed with strung conductors or rigid buses or a combination of both. Switchyards with rigid buses seem to provide the most optimum and cost-effective solution.

Switchyards are located at:

Generating Stations – where the power is evacuated. Over a period, with the expansion of the power plant (installing additional generating units) the voltage of evacuation may increase. It is not uncommon for a generating station to evacuate power at different voltages.